Air filter bag

ABSTRACT

An improved air filter bag comprising a height from about 35 cm to about 50 cm; a nominal diameter from about 10 to about 40 cm; and a first taper angle from about 65° to about 83° is provided.

FIELD OF THE INVENTION

The present invention is directed to an air filter bag that filters dustand particulates from an incoming air stream to reduce particulates inthe filtered airstream.

BACKGROUND OF THE INVENTION

Air includes many pollutants such as odors (e.g. cigarette smoke), VOCs,microbials (e.g. bacteria, viruses, mold), particulates (e.g. dust),that have a pernicious effect when inhaled or otherwise contacted byhuman beings. Particulates alone comprise dead skin, pet dander, dustmite feces, and other microscopic (less than 5 microns in size)particulates which may elicit a human immune response.

There are several air filters and air filtering devices known in the artthat are intended to remove particulates from the air. Often times, suchair filtering devices employ planar air filters for filteringparticulates. U.S. Pat. No. 4,336,035 discloses tapered filter bags forindustrial application with specified sizes of the filter bags (e.g. topradius, bottom radius, bag length). U.S. Pat. No. 7,832,567, EP 0979669,and GB 817011 also disclose tapered filter bags for industrialapplications but do not specify any sizes or taper angles. One drawbackwith previous air filtering bags may be air flow through the air filterbag.

Accordingly, there continues to be a need for an improved air filter bagand method of filtering air which cost-effectively removes particulatesfrom the air and includes consumer-friendly features such as ease ofuse.

SUMMARY OF THE INVENTION

According to one embodiment of the invention, there is provided an airfilter bag comprising a height from about 35 cm to about 50 cm; anominal diameter from about 10 to about 40 cm; and a first taper anglefrom about 65° to about 83°.

According to another embodiment of the invention, there is provided anair filter bag comprising a height from about 35 cm to about 50 cm; anominal diameter from about 10 to about 40 cm; a first taper angle; agusset comprising a gusset taper angle from about 42° to about 48° and adepth of less than about 10.2 cm.

According to yet another embodiment of the invention, there is providedan air filter a height from about 35 cm to about 50 cm; a nominaldiameter from about 10 to about 40 cm; a first taper angle from about78° to about 83°; a gusset comprising a gusset taper angle from about 42to about 48° and a depth of less than about 10.2 cm; wherein said airfilter bag is made from a non-woven having a thickness between about 1and about 3 mm, a density from about 20 kg/m³ to about 60 kg/m³, and apore volume distribution of at least about 15% of the total volume is inpores of radii less than about 50 μm, at least 40% of the total volumeis in pores of radii between about 50 μm and about 100 μm, and at least10% of the total volume is in pores of radii greater than about 200 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with the claims particularly pointingout and distinctly claiming the invention, it is believed that thepresent invention will be better understood from the followingdescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 shows one embodiment of an air filtering the device in accordancewith the present invention;

FIG. 2 shows a cross-sectional view of the air filtering device in FIG.1;

FIG. 3 shows an exploded view of the air filtering device in FIG. 1;

FIG. 4 shows the cross-sectional view of the device in FIG. 2, showingonly the base of the device (i.e. device with the outer sleeve, airfilter, and related parts removed);

FIG. 5 is an exploded view of the base in FIG. 4;

FIG. 6A shows one embodiment of an air filter bag in accordance with thepresent invention;

FIG. 6B shows one embodiment of an air filter bag having a gusset inaccordance with the present invention and showing the cut-line to removethe bottom portion with the attachment member;

FIG. 6C shows one embodiment of an air filter bag without a gusset inaccordance with the present invention and showing the cut-line to removethe bottom portion with the attachment member;

FIG. 7A shows a cut-away section of the outer sleeve, taken along lineLA in FIGS. 1 and 2; FIG. 7B shows another embodiment of an outer sleevein accordance with the present invention;

FIG. 8 is a graph showing the static pressure and air flow rates of anair filtering device, in accordance with the present invention, and thepressure drops within the device associated with having varying spatialgaps between the air filter and outer sleeve.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-3, an exemplary embodiment of a device 10 forfiltering air is shown. The device 10 may include a base 20, a fan 40functionally attached to the base, an air filter bag 50 releasablyattached to the base, and a substantially air impermeable outer sleeve80. The device 10 may be powered by replaceable or rechargeablebatteries, an AC outlet (directly AC driven or an adequate AC to DCpower supply), a car DC power source, a solar cell, or the like.

As input air having particulates or other contaminants, which may rangein size from about 0.1 microns to about 30 microns, enters the device10, the input air is filtered through the air filter bag 50, thusreducing particulates in the output air.

The air filter bag 50 of the present invention longitudinally extendsfrom the base 20 and is in air flow communication with the air outlet 24of the base 20. The air filter bag 50 may include at least oneattachment member 52 which releasably attaches the air filter bag 50 tothe base 20. The attachment member 52 may include clips, elastic bands,gripping materials, hook and loop fasteners, and the like. Attachmentmember 52 may also include chemical (e.g. removable adhesive), magnetic,or static cling elements. One fastening approach is to provide a tabthat engages a mechanical switch that is electrically connected to thefan 40 to power it on when the air filter 50 is properly engaged.

The construction of the attachment member 52 will result in the airfilter bag 50 having a gathered or non-gathered opening. To determine ifthe air filter bag 50 has a gathered or non-gathered opening, one canmeasure the circumference of the air filter opening 54 with and withoutthe attachment member 52. If the circumference of the air filter opening54 without the attachment member is greater than about 5% of thecircumference of the air filter opening with the attachment member, theair filter bag 50 is considered to have a gathered opening. If thecircumference of the air filter opening without the attachment member issubstantially the same (i.e. less than or equally to about 5% as thecircumference of the air filter opening with the attachment member), theair filter bag 50 is considered to have a non-gathered opening. Onemethod of creating a gathered opening is to attach a tensioned elasticband around the opening 54 of the air filter bag 50 and then release thetensioning of the elastic band.

The air filter bag 50 may have an air flow surface area of about 0.1 m²to about 1 m² (about 1.08 ft² to about 10.76 ft²), or about 0.1 m² toabout 0.6 m² (about 1.08. ft² to about 6.46 ft²), or about 0.15 m² toabout 0.5 m² (about 1.61 ft² to about 5.38 ft²), or about 0.2 m² toabout 0.4 m² (about 2.15 ft² to about 4.31 ft²). The air flow surfacearea, as used herein, is the permeable area from which air flows throughthe air filter bag 50. This air flow surface area is measured by layingthe air filter bag 50 out flat on a single plane without any folds orpleats and then measuring the total surface area. The measured air flowsurface area of the air filter bag 50 may not include any areas where aphysical or chemical barrier (e.g. a structure or coating on an edge ofthe filter) prevents air flow through that part of the air filter. Usingan air filter with more air flow surface area may be desirable as itenables a lower face velocity of air through the air filter bag 50 whichlowers the pressure drop. This enables a higher air flow rate (i.e. CFM)from the fan 40 for a given amount of power. Higher air flow surfacearea also enables a quieter device since less power is needed from thefan 40.

The air filter bag 50 of the present invention may have an average facevelocity of about 6 fpm to about 60 fpm (about 1.83 m/min to about 18.29m/min), or about 25 fpm to about 50 fpm (about 7.62 m/min to about 15.24m/min), or about 25 to about 40 fpm (about 7.62 m/min to about 12.19m/min) In one embodiment, the air filter face velocity is about 36 fpm(about 10.97 m/min). Air filter face velocity is the velocity of air asit exits the outer face of the air filter bag 50. The air filter bag'souter face is downstream of the air filter bag's inner face such thatair flows from the inner face to the outer face of the air filter bag50. In configurations where air is routed directly from the fan to theair filter bag (i.e. air does not escape between the fan and an entrancepoint to air filter), as in the present invention, air filter facevelocity is calculated:

${{Filter}\mspace{14mu} {Face}\mspace{14mu} {Velocity}} = \frac{{Volumetric}\mspace{14mu} {Flow}\mspace{14mu} {rate}\mspace{14mu} ({CFM})\mspace{14mu} {through}\mspace{14mu} {the}\mspace{14mu} {air}\mspace{14mu} {inlet}\mspace{14mu} {of}\mspace{14mu} {fan}}{{Airflow}\mspace{14mu} {surface}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {air}\mspace{14mu} {filter}\mspace{14mu} \left( {ft}^{2} \right)}$

The air filter bag 50 of the present invention may be formed from asingle fibrous layer or multiple layers. The air filter bag 50 maycomprise a non-woven. “Non-woven”, as used herein and as defined byEDANA (European Disposables and Non-woven Association) means a sheet offibers, continuous filaments, or chopped yarn of any nature or origin,that have been formed into a web by means, and bonded together by anymeans, with the exception of weaving or knitting. The non-woven may becomposed of synthetic fibers or filaments or natural fibers or fiberspost-consumer recycled material such as polyolefins (e.g., polyethyleneand polypropylene), polyesters, polyamides, synthetic cellulosics (e.g.,RAYON®), and blends thereof. Also useful are natural fibers, such ascotton or blends thereof. Non-limiting examples of how the non-woven canbe formed include meltblowing, carded spunlace, carded resin bonding,needle punch, wet laid, air laid, spunbond, and combinations thereof. Anon-woven air filter may have a basis weight of about 20 to about 120gsm, where the basis weight of the non-woven or filter media is measuredaccording to the following method that follows a modified EDANA 40.390(February 1996) method.

-   -   1. Cut at least 3 pieces of the non-woven or filter media to        specific known dimensions, preferably using a pre-cut metal die        and die press. Each test piece typically has an area of at least        0.01 m².    -   2. Use a balance to determine the mass of each test piece in        grams; calculate basis weight (mass per unit area), in grams per        square meter (“gsm”) using:

${{Basis}\mspace{14mu} {Weight}} = \frac{{Mass}\mspace{14mu} {of}\mspace{14mu} {Test}\mspace{14mu} {Piece}\mspace{14mu} (g)}{{Area}\mspace{14mu} {of}\mspace{14mu} {Test}\mspace{14mu} {Piece}\mspace{14mu} \left( m^{2} \right)}$

-   -   3. Report the numerical average basis weight for all test        pieces.    -   4. If only a limited amount of non-woven or filter media is        available, basis weight may be measured and reported as the        basis weight of one piece, the largest rectangle possible.

The air filter bag 50 according to the present invention may be madeaccording to commonly assigned U.S. Pat. Nos. 6,305,046; 6,484,346;6,561,354; 6,645,604; 6,651,290; 6,777,064; 6,790,794; 6,797,357;6,936,330; D409,343; D423,742; D489,537; D498,930; D499,887; D501,609;D511,251 and/or D615,378. The degree of hydrophobicity or hydrophilicityof the fibers may be optimized depending upon the desired goal of theair filter, either in terms of type of particulate or malodor to beremoved, the type of additive that is provided, biodegradability,availability, and combinations of such considerations. In oneembodiment, the air filter bag 50 is a three layer non-woven comprisinga pre-filter layer, a functional layer and a support layer. In thisapproach, the pre-filter layer is on the upstream side of the air filterbag 50 and acts as screen for larger particulates (e.g. greater than 10microns). “Upstream”, as used herein, means a position in an air flowpath 90 that is earlier in time from a referenced position, whenmeasuring air flow through an air filtering device. The pre-filter layeris comprised of a high loft structure including hydroentangledpolyester, polypropylene (“PP”), or mixtures thereof. The functionallayer catches smaller particles (e.g. less than about 2.5 microns) andmay serve as the layer comprising any malodor treatment agents. Thefunctional layer may be made from melt-blown or spun-bonded non-woven.The support layer may include high contrast bonded/unbonded areas forvisual indication of the air filter collecting particles. The supportinglayer provides the structure/rigidity desired for the air filter bag 50.The supporting layer may be made from scrim or aperture film.

The type of non-woven and manufacturing method chosen may have a largeimpact on air filter efficiency and on pressure drop and, in turn,pressure needed from the fan 40 to deliver about 50 to about 150 cubicfeet per minute (“CFM”) of air from the device 10. One material withsuitable filtering and low pressure drop is a 60 gsm hydroentanglednon-woven comprised of polyethylene terephthalate (“PET”) fibers with a10-20 gsm spunbond PP layer to provide structure/support for thehydroentangled PET fibers (collectively referred to herein as “60 gsmHET”). With the hydroentangling process, one can achieve a 1 mm to 3 mmthickness with this construction which enables a lower pressure drop forthe same basis weight. Thickness is measured according to the followingmethod that follows a modified EDANA 30.5-90 (February 1996) method.

-   -   1. Equipment set-up should include        -   a. Foot Diameter: 40.54 mm (1.596 inch)        -   b. Foot Area: 12.90 cm² (2 in²)        -   c. Foot Weight: 90.72 grams (0.2 lbs)        -   d. Foot Pressure: 7.03 grams/cm² (0.1 psi, 0.69 kPa)        -   e. Dwell time: 10 s    -   2. Measure at least 4 locations, ideally 10. All should be        single layer and without creases. Do not smooth, iron or tension        the material to remove creases. Test pieces need to be larger        than the area of the pressure foot    -   3. Place the uncreased sample under the pressure foot for dwell        time and measure thickness in mm    -   4. Report the numerical average for all test pieces.

It has been found that an air filter density of less than about 60 kg/m³may be desired to provide meaningful efficiency while also having lowpressure drop. With the 60 gsm HET material, a density from about 20 toabout 60 kg/m³ may be provided. This results in a non-woven thatdelivers good air filter efficiency and low pressure drop for the device10 described herein. This is because the fibers are spread out throughthe thickness enabling more air flow pathways, resulting in less fiberto fiber contact and more available fiber surface area to captureparticles. Other ways to achieve thickness for a given basis weightinclude but are not limited to through air bonding, airlaid, needlepunching, and carded resin bonded materials. The density of the airfilter bag 50 is calculated using the following equation:

${{filter}\mspace{14mu} {density}} = \frac{{basis}\mspace{14mu} {weight}\mspace{14mu} \left( \frac{g}{m^{2}} \right)}{{thickness}\mspace{14mu} (m)}$

Another non-woven with good filtering but higher pressure drop is a 59gsm spun bond/melt-blown/spun bond (“SMS”) laminate comprising 10 gsm PPspun bond, bonded to a 34 gsm PP melt-blown, bonded to another 17 gsm PPspunbond non-woven (collectively referred to herein as “59 SMS”). Bothmaterials have a similar basis weight but have very differentthicknesses and densities and, hence, pressure drops. The 60 gsm HETmaterial has a thickness from about 1 mm to about 3 mm, whereas the 59SMS structure has a thickness less than about 1 mm, resulting in adensity greater than 60 kg/m³. The 60 gsm HET material has a lowersingle pass efficiency but also has a pressure drop that is 2 to 3 timeslower enabling a higher air flow rate, lower noise, or less powerrequired for a given fan. The 60 gsm HET material or any material with adensity less than about 60 kg/m³ also has the advantage of being able tohold more dirt/particulates than a more dense filter, such as amelt-blown or SMS material, before it starts to restrict air flow thatagain could impact air flow rate for a fan over the life of the airfilter bag 50.

The pore volume distribution of the non-woven characterizes the porosityof the non-woven. It has been found that a non-woven with a preferablepore volume distribution has at least about 15% of the total volume inpores of radii less than about 50 μm, at least about 40% of the totalvolume in pores of radii between about 50 μm to about 100 μm, and atleast about 10% of the total volume in pores of radii greater than about200 μm, where the pore volume distribution is calculated usingmeasurements from the Cumulative Pore Volume Test Method shown below.

Cumulative Pore Volume Test Method

The following test method is conducted on samples that have beenconditioned at a temperature of 23° C.±2.0° C. and a relative humidityof 45%±10% for a minimum of 12 hours prior to the test. All tests areconducted under the same environmental conditions and in suchconditioned room. Discard any damaged product. Do not test samples thathave defects such as wrinkles, tears, holes, and like. All instrumentsare calibrated according to manufacturer's specifications. Samplesconditioned as described herein are considered dry samples (such as “dryfibrous sheet”) for purposes of this invention. At least four samplesare measured for any given material being tested, and the results fromthose four replicates are averaged to give the final reported value.Each of the four replicate samples has dimensions of 55 mm×55 mm.

Pore volume measurements are made on a TRI/Autoporosimeter (TextileResearch Institute (TRI)/Princeton Inc. of Princeton, N.J., U.S.A.). TheTRI/Autoporosimeter is an automated computer-controlled instrument formeasuring pore volume distributions in porous materials (e.g., thevolumes of different size pores within the range from 1 to 1000 μmeffective pore radii). Computer programs such as Automated InstrumentSoftware Releases 2000.1 or 2003.1/2005.1; or Data Treatment SoftwareRelease 2000.1 (available from TRI Princeton Inc.), and spreadsheetprograms are used to capture and analyze the measured data. Moreinformation on the TRI/Autoporosimeter, its operation and datatreatments can be found in the paper: “Liquid Porosimetry: NewMethodology and Applications” by B. Miller and I. Tyomkin published inThe Journal of Colloid and Interface Science (1994), volume 162, pages163-170, incorporated here by reference.

As used in this application, porosimetry involves recording theincrement of liquid that enters or leaves a porous material as thesurrounding air pressure changes. A sample in the test chamber isexposed to precisely controlled changes in air pressure. As the airpressure increases or decreases, different size pore groups drain orabsorb liquid. Pore-size distribution or pore volume distribution canfurther be determined as the distribution of the volume of uptake ofeach pore-size group, as measured by the instrument at the correspondingpressure. The pore volume of each group is equal to this amount ofliquid, as measured by the instrument at the corresponding air pressure.Total cumulative fluid uptake is determined as the total cumulativevolume of fluid absorbed. The effective radius of a pore is related tothe pressure differential by the relationship:

Pressure differential=[(2)γ cos Θ]/effective radius

where γ=liquid surface tension, and 0=contact angle.

This method uses the above equation to calculate effective pore radiibased on the constants and equipment controlled pressures.

The automated equipment operates by changing the test chamber airpressure in user-specified increments, either by decreasing pressure(increasing pore size) to absorb liquid, or increasing pressure(decreasing pore size) to drain liquid. The liquid volume absorbed ordrained at each pressure increment is the cumulative volume for thegroup of all pores between the preceding pressure setting and thecurrent setting. The TRI/Autoporosimeter reports the pore volumecontribution to the total pore volume of the specimen, and also reportsthe volume and weight at given pressures and effective radii.Pressure-volume curves can be constructed directly from these data andthe curves are also commonly used to describe or characterize the porousmedia.

In this application of the TRI/Autoporosimeter, the liquid is a 0.2weight % solution of octylphenoxy polyethoxy ethanol (Triton X-100 fromUnion Carbide Chemical and Plastics Co. of Danbury, Conn.) in 99.8weight % distilled water (specific gravity of solution is about 1.0).The instrument calculation constants are as follows: p (density)=1g/cm³; γ (surface tension)=31 dynes/cm; cos Θ=1. A 1.2 μm MilliporeMixed Cellulose Esters Membrane (Millipore Corporation of Bedford,Mass.; Catalog # RAWP09025) is employed on the test chamber's porousplate. A plexiglass plate weighing about 32 g (supplied with theinstrument) is placed on the sample to ensure the sample rests flat onthe Millipore Filter. No additional weight is placed on the sample.

A blank condition (no sample between plexiglass plate and MilliporeFilter) is run to account for any surface and/or edge effects within thetest chamber. Any pore volume measured for this blank run is subtractedfrom the applicable pore grouping of the test sample. For the testsamples, a 4 cm×4 cm plexiglass plate weighing about 32 g (supplied withthe instrument) is placed on the sample to ensure the sample rests flaton the Millipore filter during measurement. No additional weight isplaced on the sample.

The sequence of pore sizes (pressures) for this application is asfollows (effective pore radius in μm): 10, 20, 30, 40, 50, 60, 70, 80,90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 350, 400,450, 500, 550, 600, 650, 700, 750, 800.

These pressure values are used to produce the Advancing 1 and Receding 1curves. This sequence starts with the sample dry, saturates it as thepressure decreases (i.e., Advancing 1 curve), and then subsequentlydrains the fluid out as the pressure increases again (i.e., Receding 1curve).

The TRI/Autoporosimeter measures the cumulative weight (mg) of liquid ateach pressure level, and reports the respective cumulative pore volumeof the sample. From these data and the weight of the original drysample, the ratio of cumulative pore volume/sample weight can becalculated at any measured pressure level, and reported in mm³/mg. Inthe case of this test method, the cumulative pore volume is determinedduring the Receding 1 curve, and is reported in mm³/mg and taken fromthe TRI instrument.

High thickness and low density at similar basis weights enables a filtermaterial to have good air flow while also still having a lot of fibersurface area to electrostatically attract and/or mechanically filterparticles. This electrostatic benefit can be further enhanced byleveraging PP fibers or other materials/coatings that are negativelychanged in the triboelectric series to help attract positively chargedparticles like hair, skin, and cotton. Optionally, the air filtermaterial can be electrostatically charged via corona treatment at themanufacturing site to help the material maintain a charge for attractingsmall particulates when the fan blows the air through the filtermaterial. Another approach that may deliver improved particle pick-up isionization in the device to help create a charge on the particles in theair such that the particles are attracted to the filter material whenair with particles is passed through the air filter 50 via the fan 40.

The air filter bag 50 of the present invention may have a totalaggregate basis weight of at least about 30 g/m², alternatively at leastabout 50 g/m², alternatively at least about 70 g/m². The total aggregatebasis weight of the present air filter bag 50 is typically no greaterthan about 200 g/m², alternatively no greater than about 150 g/m², andalternatively no greater than about 100 g/m². The aggregate basis weightcan be measured using the basis weight equation described previously.

The air filter bag 50 may include air treatment agents to improve theparticulate removal from the air, freshening the air, providinganti-microbial activity, and/or the like. An air freshening agent mayinclude anti-bacterial, anti-viral, or anti-allergen agents; ionic andnon-ionic surfactants; wetting agents; peroxides; ionic and non-ionicpolymers, including those described in US 2012/0183488 and US2012/0183489; metal salts; metal and metal oxides catalysts (e.g. ZPT,Cu, Ag, Zn, ZnO); pH buffering agents; biological agents includingenzymes, natural ingredients and extracts thereof; coloring agents; andperfumes, including those described in U.S. Pub. 2011/0150814, U.S. Pat.No. 8,357,359, U.S. Pub. 2013/0085204. It is also contemplated that theair treatment agent may include vitamins, herbal ingredients, or othertherapeutic or medicinal actives for the nose, throat, and/or lungs.

In some embodiments, the air filter bag 50 includes conductive materialsand/or carbon particles to help remove odors and/or trap small molecules(VOC's, etc.). The air filter bag 50 may have high porosity with asubstantially flat surface and open cells or apertures that mayrepresent greater than about 50% of the air filter, or about 50%, orabout 30%, or about 25%, or about 20%, or about 10%. The void volumewithin the air filter bag 50 may consist of tortuous channels formedwithin the material such as those found in foams, sponges, and filters.The surface area may be in the form of tortuous voids within the volumeof the air filter. The surface area to dimensional area ratio may beabout greater than about 2, alternatively greater than about 4.

The air filter bag 50 may comprise an additive. The type and level ofadditive is selected such that the air filter has the ability toeffectively remove and retain particulate material, while maintainingthe electrostatic properties of the filter and minimizing the amount ofreemission. As such, the additive may be non-cationic, as cationicadditives may tend to diminish the electrostatic properties. In oneembodiment, the air filter bag 50 is impregnated with a polymericadditive. Suitable polymeric additives include, but are not limited to,those selected from the group consisting of pressure sensitiveadhesives, tacky polymers, and mixtures thereof. Suitable pressuresensitive adhesives comprise an adhesive polymer, which is optionallyused in combination with a tackifying resin (e.g. Mirapol™ polymer),plasticizer, and/or other optional components. Suitable tacky polymersinclude, but are not limited to, polyisobutylene polymers,N-decylmethacrylate polymers, and mixtures thereof. The adhesivecharacteristics of a polymeric additive may provide effectiveparticulate removal performance. Adhesive characteristics of thepolymeric additives can be measured using a texture analyzer. A suitabletexture analyzer is commercially available from Stable Micro Systems,Ltd. in Godalming, Surrey UK under the trade name TA.XT2 TextureAnalyser.

The air filter bag 50 of the present invention may have a dirt holdingcapacity of greater than about 1 gram of dirt or about 3 to about 6grams of dirt at an air filter face velocity of 20 to 40 feet/min, whileincreasing pressure drop by less than 12.5 Pa (0.05″ water gauge), orthe increased pressure drop of the additional dirt on filter is lessthan 10 Pa, or less than 5 Pa, or less than 3.5 Pa, or less than 2 Pa.The end-of-life of the air filter bag 50 may be 30 days, 60 days, 90 ormore days. Dirt holding capacity and change in pressure drop as a resultof adding dirt are measured via a modified ASHRAE 52.1-1992 method.

-   -   1. Measure at least 2 samples of the filter media, 6 or more        preferably as prescribed by the method.    -   2. Measurements are taken on a flat filter sheet, without        pleats, wrinkle, creases, etc, at least 14″×14″. Particles are        then injected across a 1 ft diameter circle of the filter sheet.    -   3. Orient the material in the test apparatus such that particle        hit the same side of the material 1^(st) that will see particles        1^(st) in the device, if the material has different properties        depending on orientation. If the material is non-homogenous        across the area, sample representative materials.    -   4. Run the test with an air filter face velocity chosen to        closely match the air filter face velocity in the device based        on the air filter surface area used in the device and air flow        rate in the device, load to 6 grams of dirt, use ISO Fine A2        dirt (as defined in ISO 12103-1), and load in increments of        0.5 g. Measure resistance after each 0.5 g addition.

The air filter bag 50 of the present invention has a single passfiltering efficiency of about 20%-70% of E2 particles and about 50-90%of E3 particle as defined by modified single pass ASHRAE Standard 52.2method below. Single pass filtration properties of a filter may bedetermined by testing in similar manner to that described in ASHRAEStandard 52.2—2012 (“Method of Testing General Ventilation Air-CleaningDevices for Removal Efficiency by Particle Size”). The test involvesconfiguring the web as a flat sheet (e.g. without pleats, creases orfolds) installing the flat sheet into a test duct and subjecting theflat sheet to potassium chloride particles which have been dried andcharge-neutralized. A test face velocity should be chosen to closelymatch the face velocity in the device based on the filter surface areaused in the device and air flow rate in the device. An optical particlecounter may be used to measure the concentration of particles upstreamand downstream from the test filter over a series of twelve particlesize ranges. The equation:

${{Capture}\mspace{14mu} {efficiency}\mspace{14mu} (\%)} = \frac{\left( {{{upstream}\mspace{14mu} {particle}\mspace{14mu} {count}} - {{downstream}\mspace{14mu} {particle}\mspace{14mu} {count}}} \right) \times 100}{\left( {{upstream}\mspace{14mu} {particle}\mspace{14mu} {count}} \right)}$

may be used to determine capture efficiency for each particle sizerange. The minimum efficiency for each of the particle size range duringthe test is determined, and the composite minimum efficiency curve isdetermined. From the composite minimum efficiency curve, the fourefficiency values between 0.3 and 1.0 μm may be averaged to provide theE1 Minimum Composite Efficiency (MCE), the four efficiency valuesbetween 1.0 and 3.0 μm may be averaged to provide the E2 MCE, and thefour efficiency values between 3.0 and 10.0 μm may be averaged toprovide the E3 MCE. As a comparison, HEPA filters typically have asingle pass efficiency above 99% for both E2 and E3 particles.

FIG. 6A shows one possible air filter bag 150 construction and sealpattern with a gusset 66 that is very similar to a typical stand-uppouch with tapered sides, except the gusset 66 is at distal end 60 (i.e.top) versus a typical pouch where the gusset is on bottom, serving as abase to help the bag stand-up and not fall over.

The air filter bag 150 may be formed by folding and heat-sealing two ormore edges 64 of the air filter 50, creating a bag or tube-like shapewhen inflated with air. The air filter 50 may be sealed in a manner thatcreates a funnel-like shape such that it longitudinally extends from thebase 20 and follows the shape of the outer sleeve 80, but does not touchthe outer sleeve. To reduce the width at the distal end 60 and enablegood air flow between outer sleeve 80 and outer face 62 of the airfilter bag 150, a tapered seal and/or a gusset 66 at the distal end 60may be formed.

The air filter bag 150 may include side and/or top gussets that areabout 2 cm to about 10 cm, similar to stand-up pouches which are formedprior to sealing to help maintain a unique shape when inflated by fan 40and help maintain a good spatial gap for air flow between the air filterbag 150 and the outer sleeve 60. The addition of a gusset to an airfilter bag may provide a planar/flat appearance of the distal end 60 ofthe air filter bag 150 once the air filter bag is inflated. This may beimportant as it enables the air filter bag 150 to provide a clearusage/end-of-life signal to a consumer. A gusset 66 may also help ensurea predictable and uniform inflatability each time without the use ofassistance wires (such as a coil 186 shown in FIG. 7B).

One embodiment, a gusset 66 can be constructed using the followingprocess.

Horizontal Production Process

-   -   A 45 degree turn bar takes the filter web from horizontal to        vertical. Then a forming shoulder takes the vertical flat web        into a c-shape, then to an m-shape. At the exit of the forming        shoulder, there is a set of nip rolls to crease the gusset        m-fold. Next, the filter is heat-sealed from the top, sealing        the 2-layer lower section of the bag and one side of the 4-layer        gusset, followed by another heat sealing step from underneath        the web to seal the 2-layer lower section of the bag again as        well as the opposite side of the 4-layer gusset. Bonding from        both sides of the 4-layer gusset enables keeping the center        layers of the gusset from bonding together. For more robust        separation of the center layers of the gusset, any small amount        of seal formed can be delaminated by running through a        separation plate. A more robust technique to prevent bonding of        the center layers is to have a metal plate present in the center        of the gusset during heat sealing, or run a web of        silicone-coated paper, teflon coated paper, or other film        through the center of the gusset that will keep the center 2        layers of the 4 layer structure from sealing. Finally the gusset        is cut, along with the rest of the bag, using a rotary die and        anvil knife.

The air filter bag 150 may have a nominal diameter of about 10 cm toabout 40 cm, or about 10 cm to about 15 cm, or about 20 cm with anupright height of about 35 cm to about 50 cm, or about 40 cm, whenexpanded, to achieve a surface area of about 0.3 m². The heat sealededges 64 and gusset 66 form an air-tight seal, which in someembodiments, withstands more than about 40 g/cm peel force to preventdelamination and/or air flow through unsealed areas.

Now referring to FIGS. 6B and 6C, the air filter bag 50 has a height (h)in the y-direction, a first width (w_(o)) and second width (wt), both inthe x-direction and a gusset 66. It has been found that tapered sides ofan air filter bag 50 (with specified angles) improve airflow (CFM)through the air filter bag. Further, where a gusset 66 and end-of-lifesignal on the gusset is employed, the first taper angle (fw_(o)) shouldbe greater than 70 degrees to provide sufficient surface area at thedistal end 60 of the air filter bag 50 (when inflated) to support theend-of-life signal.

To keep the airflow greater than 65 CFM, the air filter bag 50 has afirst taper angle (fw_(o)) near the opening 54 of the filter bag 50which may be from about 65 to about 83 degrees, or from about 78° toabout 83°. Volumetric air flow rates of the air filter bag 50 havingvarying first taper angles can be measured using methods as described inDIN EN ISO 5801:2011-11. Table 1 shows air flow at various first taperangles and gusset taper angles.

TABLE 1 Gusset First Taper Angle (near Gusset Taper Air Flow Areaopening of bag) Angle (CFM) (cm²) (in degrees) (in degrees) 66.6 65 6585 71.8 161 71 85 75.2 165 76 60 76.3 166 77 53 77.8 129 78 48 77.1 14579 45 74.7 152 80 45 72.1 161 81 42 66.9 194 83 42 61.0 177 84 42 58.5226 86 42

In some embodiments where an end-of-life signal is employed on thedistal end 60 of the air filter bag 50, the first taper angle (fw_(o))is greater than 78° to properly accommodate the end-of-life signal andless than 83° to enable sufficient air flow for filtering particulates.

Method for measuring First Taper Angle

-   -   1. Referring to FIGS. 6B and 6C, Cut off the bottom 1 inch of        the air filter bag. If cutting off the bottom 1 inch is        insufficient to remove the attachment member, then cut off the        minimum amount required in order to achieve the removal of the        attachment member(s).    -   2. Take all measurements on the flat air filter bag (not        inflated in the device) without stretching the material. Make        sure that air filter bag is fully unfolded so that it is at its        widest dimensions without physically deforming or tearing the        air filter bag.    -   3. If the air filter bag being measured has a top gusset (gusset        at the distal end 60 of the air filter bag), proceed with Step 1        of Method A    -   4. If the air filter bag being measured has side gussets or no        gussets, proceed with Step 1 of Method B.

Method A

-   -   1. Measure the total air filter bag height (h)    -   2. Measure the gusset depth (d)    -   3. If gusset depth (d) is equal or greater than ½ of the total        filter height (h), follow Method B instead to calculate the        first taper angles. If gusset depth (d) is less than ½ of the        total filter height (h), proceed with step 4 of Method A.    -   4. Subtract gusset depth (d) from total filter height (h) to get        the height (f) for first taper angle calculation.    -   5. Measure the first width (i.e. width at the opening of the        filter) (w_(o))    -   6. Measure the gusset width (i.e. width at the proximate to the        first width) (g)    -   7. Subtract the width at the gusset (g) from the width at the        opening (w_(o)) and divide by 2 to get the base (b) for the        first taper angle    -   8. First taper angle is tan⁻¹(f/b) in degrees

Method B

-   -   1. Measure the total air filter bag height to get the height        (h′) for first taper angle.    -   2. Measure the width at the opening of the filter (w_(o)′)    -   3. Measure the second width (i.e. distal end of the filter)        (w_(t)′)    -   4. Subtract the second width (w_(t)′) from the first width        (w_(o)′) and divide by 2 to get the base (b′) for the first        taper angle    -   5. Filter first taper angle is tan⁻¹(h/b′) in degrees

Method for Measuring Gusset Taper Angle

-   -   1. Referring to FIG. 6B, cut off the bottom 1 inch of the air        filter bag. If cutting off the bottom 1 inch is insufficient to        remove the attachment member(s), then cut off the minimum amount        required in order to achieve the removal of the attachment        member(s).    -   2. Take all measurements on the flat air filter bag (not        inflated in the device) without stretching the material. Make        sure that air filter bag is fully unfolded so that it is at its        widest dimensions without physically deforming or tearing the        air filter bag.    -   3. Measure gusset depth (d)    -   4. Measure the gusset width (g)    -   5. Measure the second width (w_(t))    -   6. Subtract the second width (w_(t)) from the gusset width (g)        and divide by 2 to get the gusset base (b″) for the gusset taper        angle    -   7. Gusset taper angle is tan⁻¹(d/b″) in degrees

Sensors (not shown), chemical or physical in kind, may be used toindicate end-of life of the air filter bag 50 (i.e. the need for airfilter replacement) and/or monitor the quality of air entering andexiting device 10. One approach of providing an end-of-life sensor iswith a white or clear tape that is added to the air filter bag 50. Thetape may be the same color as the starting color of the air filter 50such that it is not visible when new but as the air filter accumulatesparticulates and becomes dirty, a consumer can visually see a contrastfrom the aging/dirty filter to the original filter color. Anotherapproach for providing an end-of-life air filter is to heat-seal thefibers of the air filter bag 50 with a unique pattern such that there isno air flow through the heat-sealed portion of the air filter bag 50.This heat-sealed portion can be any desired shape and can be coloredwith ink to match the original starting color as needed. Anotherapproach for an end-of-life signal is to provide filter tabs that engagethe device to start a timer that turns on a LED or similar light orsound to remind consumer to change filter. Another unique approach is toprovide a “snooze” button that enables or reminds users to check againafter some set desired time (1 week, 1 month, etc. . . . ).

The air filter bag 50 may be used on an air filter device 10 as shown inFIGS. 1-5. The device 10 may be sized such that it can be used on atable top or in a living space such as a room having about 22 m³ toabout 75 m³ of space. The device 10 may have a smaller footprint thanits upright height along the longitudinal axis LA to be suitable forsmall spaces. For example, when in its upright position, the device maybe about 20 cm to about 30 cm wide, about 20 cm to about 30 cm deep, andabout 45 cm to about 75 cm tall along the longitudinal axis LA. Theheight of the device 10 may be reduced during storage where collapsibleparts are used.

The device 10 may be characterized by air flow, air filter properties,and device configuration (e.g. housing, grill covers, air filter, andouter sleeve configuration). Such aspects lead to a pressure drop withinthe device 10. In one embodiment, the device 10 may result in a totalpressure drop of about 15 Pa to about 25 Pa, or about 8 Pa to about 20Pa. Other embodiments may have higher or lower pressure drops leading tohigher or lower air flow requirements for the fan 40 in order to lead tothe same air flow of the device 10.

Referring to FIGS. 4-5, a device 10 suitable for use with the air filterbag 50 may include a base 20 constructed of any known material tostabilize a motorized fan 40. The base 20 may include a fan housing 30and legs 32 supporting the fan housing and raising the fan housing froma supporting surface to facilitate air flow into an air inlet 22 whenthe air inlet is located an on underside of the base. The base 20, withlegs 32, may be about 5 cm to about 10 cm tall and about 20 cm to about30 cm in diameter to reduce part weight. The base 20 has an air inlet 22on a first side 23 of the base and an air outlet 24 on a second side 25of the base. In some embodiments, the base 20 may include grill covers26 a, 26 b corresponding to the air inlet 22 and air outlet 24, and,optionally, a fan pre-filter 42 and fan cover 44 for filtering largeparticles (e.g. hair) to help keep the fan clean.

The base 20 may have a tapered shroud 34 with a first step 36 to enableattachment of an air filter 50 and a second step 38 for attachment of anouter sleeve 80. The second step 38 may be lower on the shroud 34 of thebase 20, circumferencing the first step 36. The shroud 34 may have adiameter at the top of about 16 cm to about 25 cm, expanding downward toabout 20 cm to about 30 cm.

A fan 40 is functionally attached to the base 20 such that it assistswith drawing a volume of input air into the air inlet 22 of the base andout through the air outlet 24, pushing the volume of air through an airflow path 90 defined by the outer sleeve 80 and through the air filter50, also located in the air flow path 90. The fan 40 may be mountedinside the base 20 between the first side 23 and the second side 25 ofthe base 20. In some embodiments, the fan 40 can be placed downstream ofan air filter 50 such that a volume of air is pulled through an airfilter (vs. pushed through the air filter) and the air filter cleans theair before passing over the fan 40. “Downstream”, as used herein, meansa position in an airflow path that is later in time from a referencedposition, when measuring air flow through an air filtering device.

The fan 40 may include a fan blade and motor. The rotating fan blade maybe at least about 5 cm from the surface upon which the device 10 reststo avoid a high pressure drop in urging air into the air flow path 90and also to minimize drawing in undesirable quantities of debris (e.g.dirt/hair). The fan 40 may be activated or powered by a power sourceproviding less than about 25 Watts, or less than about 15 Watts, or lessthan about 8 Watts, or less than about 6 Watts of power to the fan.

The fan 40 may be set at a predetermined speed to provide a desired airflow rate or may be set by a control having user-selected speeds. Thefan 40, when activated without the air filter 50 or outer sleeve 80, mayprovide from about 70 to about 150 CFM, or about 85 to about 130 CFM, orabout 100 to about 120 CFM, of air.

In one embodiment, an axial fan is mounted in the base 20. Where anaxial fan is used, the desired axial fan blade (also called impeller)diameter can be measured from tip to tip at outer most point of theblade and may have a diameter of about 10 cm to about 25 cm, or about 15cm to about 25 cm, or about 17 cm to about 20 cm, and is combined withan AC or DC motor, fan housing 30, and fan speed that delivers, withoutthe air filter 50 or outer sleeve 80, about 70 to about 150 CFM, orabout 85 to about 130 CFM, or about 100 to about 120 CFM, of air.Suitable axial fans include Silverstone S1803212HN available from ConradElectronics, Orion OD180APL-12LTB available from Allied Electronics, andEBM Pabst 6212 NM available from RS Components Intl. Axial fans may besignificantly quieter than centrifugal fans typically used in airfiltering devices.

Referring again to FIGS. 1-3, the device 10 includes an outer sleeve 80longitudinally extending from the base 20. The outer sleeve 80 comprisesa first open end 82 into which air enters, a second open end 84 fromwhich air exits, and an air flow path 90 therebetween. The outer sleeve80 is releasably attached to the base 20 at the first open end 82 and,thus, in air flow communication with the air outlet 24. The outer sleeve80 envelops the air filter 50 around its longitudinal axis LA. In thisway, the direction of air flow in the air flow path 90 generally alignswith the longitudinal axis LA of the air filter 50 and outer sleeve 80.While the outer sleeve 80 shown in FIGS. 1-3 aligns with thelongitudinal axis of the device and air filter, it is contemplated thatthe second open end 84 of the outer sleeve may slightly curve away fromthe longitudinal axis LA, wherein the second open is angled about 15 toabout 30 degrees from the longitudinal axis.

The outer sleeve 80 may have a diameter at the first open end 82 andsecond open end 84 of about 7 cm to 25 cm, or about 7 cm to about 23 cm,or about 7 cm to about 17 cm, or about 7 cm to about 15 cm. The secondopen 84 end may be smaller than the first open end 82 where the outersleeve 80 is tapered at the second end. The outer sleeve 80 may beelongate—longer along the longitudinal axis LA compared to its depth andwidth. The outer sleeve 80 may be longer along the longitudinal axis LAthan the air filter 50 to assist with capturing air flow through the airfilter. In one embodiment, the outer sleeve 80 may have a length about50 cm along the longitudinal axis LA. The outer sleeve 80 may be about 1cm to about 8 cm longer than air filter 50 to capture air flow exitingthe air filter 50 and directing the air downstream at a velocity thatwill encourage full room circulation.

The outer sleeve 80 may be made of any suitable material that issubstantially impermeable to air. Substantially impermeable, as usedherein, means the volume of air exiting the outer sleeve at the secondopen end 84 is at least about 60% of the air entering the outer sleeveat the first open end 82 when the device is in use (i.e. fan isoperating). In some embodiments, the outer sleeve 80 is air impermeablesuch that the volume of air entering the outer sleeve is equivalent tothe volume of air exiting the outer sleeve. Additionally, in someembodiments, the outer sleeve 80 may be made of a flexible material,such as woven fabrics used in upholstery or outdoor furniture orumbrellas, non-wovens, polyethylene, polyvinyl chloride, acrylic, or thelike, that is capable of collapsing to a generally flat configuration orto less than about 30% of its upright configuration for ease of storageand/or shipment.

It has been learned that there is some advantage of having some lowlevel of permeability of the outer sleeve to provide air dampening. Theouter sleeve 80 has between 10 and 40% of the air passing through theouter sleeve to help dampen the sounds from the fan, filter, devicesystem.

In addition or alternatively the outer sleeve 80 may be made from a softand flexible or collapsible fabric like material such as felt, outdoorfurniture fabrics, upholstery fabrics, non-wovens and other not rigidmaterials that helps dampen the sound and being somewhat absorbent ofvibrations. This is notably different than most air cleaning systemsthat use rigid injection molded plastics as the housing and means fordirecting air and/or sealing around filter.

Now referring to FIGS. 7 a and 7 b, the outer sleeve 80 may comprise aframe 86 (which includes hinged frames or assembled frames by the userto aid in collapsing for storage) to hold the outer sleeve 80 in anupright configuration. The hinged frame 86 and the flexible material ofthe outer sleeve 80 can be optionally folded or compressed flat orrolled to enable compact design for storage. In other embodiments, theouter sleeve 80 is frameless (i.e. free of a longitudinally extendingframe). In such embodiments, the outer sleeve 80 may be made of aflexible material that includes an integral coil 186 (as shown in FIG.7B). Alternatively, the outer sleeve 80 may be frameless and made fromflexible, spring-like material that enables the outer sleeve toautomatically expand into an upright position (i.e. not collapse) whenthe outer sleeve 80 is not compressed into a collapsed configuration bythe user or in packaging. Suitable materials that are at leastsubstantially impermeable to air, flexible and spring-like includesilicon, elastic fabrics, non-wovens. The material may be 0.25 mm toabout 5 mm thick. The collapsibility of the outer sleeve 80 enables thedevice 10 to be packaged in a 26 cm×26 cm×15 cm to a 26 cm×41 cm×15 cmouter package.

Additionally, a sensor may measure air quality. The air quality sensorcan be used to turn-on the device 10 or increase the fan speed. The airquality sensor can be disposed proximate to the air inlet 22. Thecombination of the air quality sensor at the air inlet 22 and the secondopen end 84 can provide consumers with clear signal of the device'sperformance and demonstrate its efficacy.

A sensor may also be used to determine the device's orientation, haltingits operation if the device 10, for example, is not upright. A sensormay also be used to assess the air flow across device 10 to halt itsoperation if air inlet 22 or air outlet 24 is blocked or there is amalfunction of a fan 40.

The device 10 may include a re-usable or disposable fan pre-filter 42housed by a fan pre-filter cover 44. The fan pre-filter 42 may beconstructed from a reticulated foam, a screen, or variety of othermechanical means to keep large particles or other materials fromaccumulating on fan blades or motor. The fan pre-filter 42, when used,is placed upstream of the fan 40 to keep fan blades clean.

Performance

The exit velocity of air leaving the air filter bag 50 when used with anair filtering device 10 is also important to provide good aircirculation in a room such that filtering will occur in a larger space.For a medium sized room (approx 80 to 140 ft² with an 8 to 9 ftceiling), an exit velocity greater than about 0.4 meters per second(“m/s”) is desired to move 1 to 10 micron size air-borne particles tothe device with air flow in the room. For a larger room (approx. 150-225ft² with an 8 to 9 foot ceiling), an exit velocity of about 0.6 m/s orgreater is desired. With these velocities the goal is to achieve a roomair flow velocity in a significant part of the room that is greater than0.003 m/s to move airborne particles between 1 to 10 microns to thedevice where they can be removed by the filter.

Air flow rates in room that are between about 0.003 m/s and about 0.25m/s are believed good flow rates that will move air-borne particles tothe device while also providing good comfort and not providing draftlike air movement that might be less desirable by room occupants. Thiscan be achieved when the air flow out of the device 10 is from about 50to about 150 CFM with an exit velocity of air exiting the exit orificeor second open end 84 may be from about 0.5 m/s to about 3.0 m/s, orfrom about 0.6 m/s to about 2.6 m/s, or from about 0.7 m/s to about 2.0m/s. While the fan 40 configuration and the RPM of the fan affects CFMof air, other variables impacting CFM of the device 10 include: airfilter surface area, pressure drop of filter media, fan pre-filters,spatial gap between filter and outer sleeve, permeability of outersleeve, and air flow path upstream and downstream of the fan. Thisresults in an air flow rate of the complete device 10 from about 50 toabout 150 CFM, or about 60 to about 100 CFM, or about 70 to about 90CFM. Where the outer sleeve 80 is completely air impermeable and has anair-tight connection to the base 20, the exit velocity of air exitingthe second open end 84 of the outer sleeve 80 can be calculated usingthe below equation.

$\frac{{Air}\mspace{14mu} {flow}\mspace{14mu} {measured}\mspace{14mu} {CFM}\mspace{14mu} {at}\mspace{14mu} {the}\mspace{14mu} {fan}\mspace{14mu} {inlet}}{{Area}\mspace{14mu} {of}\mspace{14mu} {exit}\mspace{14mu} {orifice}\mspace{14mu} {in}\mspace{14mu} \left( {ft}^{2} \right)}$

Table 2 shows exit velocities using the above calculation.

TABLE 2 Exit Exit CFM Diameter Velocity ft3/min inches ft/sec m/sec 50 64.24 1.29 50 8 2.38 0.72 50 10 1.52 0.46 75 6 6.36 1.94 75 8 3.58 1.0975 10 2.29 0.69 100 6 8.49 2.58 100 8 4.77 1.45 100 10 3.05 0.93 150 612.73 3.88 150 8 7.16 2.18 150 10 4.58 1.39

When the outer sleeve 80 and outer sleeve to base 20 connection iscompletely impermeable, one can use a mass balance with volumetric airflow into fan equal to volumetric flow out thru the exit orifice. Theexit orifice used in calculations for exit velocity should be the areaof the final area of the device as the air is leaving the device (hence,handles in a top ring handle and/or other obstructions should be notused in the area calculation).

Where the outer sleeve 80 is partially permeable to air, the exitvelocity of air exiting the second open end 84 of the outer sleeve canbe calculated using the following equation:

Exiting Airflow Through Second Open End of Outer Sleeve (in CFM)+Area ofExit Orifice (in Ft²)

To maintain efficient air flow with minimal pressure drop through theair filter bag 50, the outer sleeve 80 is positioned radially outwardlyfrom the air filter bag 50, forming a spatial gap 100. The spatial gap100 provides a pressure a drop of less than about 8 Pa, or less thanabout 6 Pa, or less than about 4 Pa, or less than about 2 Pa at 80 to120 CFM of air. The air filter bag 50 and the outer sleeve 80 may takeon any desired shape (e.g. cylindrical air filter bag circumferentiallysurrounded by a cylindrical outer sleeve or a squared outer sleeve,etc.). In some embodiments, the spatial gap 100 may be about 3 mm toabout 5 mm, or at least 3 mm, or about 12 mm to about 30 mm, or greaterthan about 20 mm from the air flow surface area of the air filter 50 tothe outer sleeve 80. The air flow surface area may include a lowerregion positioned proximal to the attachment member 52 and an upperregion distally located from the attachment member. Where the fan 40provides a CFM between about 80 to about 100, a suitable minimal spatialgap may be at least about 3 mm at the lower region and the minimumspatial gap at the distal upper region may be at least about 15 mm. Thespatial gap 100 enables more air flow through the air filter bag 50. Ifthe gap is too small, air flow through the air filter may be minimizedcausing a reduction in CFM from the device 10.

The pressure drop of the air filter bag 50 when used with the device 10(the device may include the housing, outer sleeve, base, grills, fan,fan pre-filter, and any other components that might limit air flow) isbetween about 5 and about 25 Pa. A device with a HEPA or HEPA-likefilter will typically have a pressure drop much greater than 25 Pa atflow rates greater than 70 CFM. This higher pressure drop results inhigher power consumption, typically greater than 25 Watts, in order todeliver greater than 70 CFM with the HEPA or HEPA-like filter. Hence,with the present invention, a fan 40 may be selected that will deliverabout 50 to about 150 CFM, while under about 5 to about 25 Pa pressuredrop from this device while also keeping the noise of the total deviceto be less than about 50 dB(A) per the Sound Power measurement describedherein, while also operating at a low power consumption of less than 25Watts.

The air filter bag 50 when used with an air filtering device 10 mayfilter greater than 30% or from about 40% to about 70% of particulatesthat are substantially about 0.3 microns to about 10 microns in size; in20-40 minutes; with a total pressure drop of the device less than about75 Pa, or less than about 25 Pa, or less than about 20 Pa, or less thanabout 10 Pa, or less than about 9 Pa; at an air exit velocity from about0.1 to about 4.0 m/s, or from about 0.5 m/s to about 3 m/s, or about 0.8m/s to about 3 m/s, or about 0.8 m/s to about 2.6 m/s, or about 0.6 m/sto about 2.6 m/s, or about 0.8 m/s to about 1.8 m/s, or about 0.7 m/s toabout 2.0 m/s); and an air flow rate greater than about 70 CFM, or fromabout 70 CFM to about 150 CFM. For particles that are greater than 1microns, the device 10 of the present invention can filter greater than50% of particles in 20 minutes; with a pressure drop within the deviceof less than about 25 Pa, or less than about 15 Pa, or less than about10 Pa; at an exit velocity of about 0.5 m/s to about 3 m/s; and an airflow rate greater than 70 CFM, or from about 70 FM to about 150 CFM.Filtering efficiency of an air filtering device can be determined byusing the method described in ANSI/AHAM-1-2006).

Examples Effect of Varying Spatial Gaps

Four air filtering devices are constructed: (1) a 23 cm×23 cm×66 cmouter sleeve device having an air filter bag in which about 30% of theair flow surface area is in contact with the outer sleeve; (2) a25×25×66 cm outer sleeve device and (3) a 30×30×66 cm outer sleevedevice both having air filter bags that do not touch the outer sleeve(the latter having a larger spatial gap between the air filter bag andthe inside wall of the outer sleeve than the former); and (4) a devicewithout an outer sleeve. The larger the spatial gap, the lower thepressure drop. Although no outer sleeve is beneficial with respect topressure drop, lacking an outer sleeve has inferior performance incapturing enough air to provide the necessary exit velocities for thedevice to filter air in a room.

The four constructed devices are operated with the same fan—four Noctua12 V fans—providing 80 to 120 CFM of air at 4 to 8 Pa. The air flow andpressure can be calculated by testing the device with the fan using themethods described in DIN EN ISO 5801:2011-11. In the test, the air inletside of the fan or the inlet side of the device (fan, air filter, outersleeve assembly) or the inlet side of the system (fan, filter, sleeveassembly) is attached to the testing rig, blowing the air outwardly fromthe testing rig to a free space.

FIG. 8 shows the relationship between the quantity of air (i.e. CFM) thefan delivers and the pressure generated at various air quantities. CFMis presented along the x-axis. Pressure, the term used to identify the“push” needed to overcome the system's resistance to airflow, ispresented along the y-axis. Typically, for a given fan power, as backpressure increases, flow rate decreases. This curve is constructed byplotting a series of pressure points versus specific flow rates.

FIG. 8 also shows the characteristic of the present four fan device anddifferent air flow resistances. These different air flow resistances aregenerated by different spatial gaps around the air filter. The highestflow rate will be achieved without any additional parts like an outersleeve around the filter. Outside the filter is only free air, but thereis no direction of air flow defined without an outer sleeve. An outersleeve will guide the air flow in a defined direction and will increasethe air flow resistance and, with that, the pressure drops inside thedevice. A smaller spatial gap between outer sleeve and filter increasesthe air velocity but reduces the air flow. It is necessary to optimizethese parameters (air velocity, flow rate, pressure drop) to obtain anair flow which is able to fulfill the requirements in terms of filteringperformance. As seen in FIG. 9, the smallest outer sleeve—23 cm×23 cm×66cm—throttles down the air flow because the spatial gap is nearly zero inmost of gap areas between the outer face of the air filter and theinside surface of the outer sleeve.

Throughout this specification, components referred to in the singularare to be understood as referring to both a single or plural of suchcomponent.

Every numerical range given throughout this specification will includeevery narrower numerical range that falls within such broader numericalrange, as if such narrower numerical range were all expressly writtenherein. Further, the dimensions and values disclosed herein are not tobe understood as being strictly limited to the exact numerical valuesrecited. Instead, unless otherwise specified, each such dimension isintended to mean both the recited value and a functionally equivalentrange surrounding that value. For example, a dimension disclosed as “40mm” is intended to mean “about 40 mm”

Every document cited herein, including any cross referenced or relatedpatent or application is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. An air filter bag comprising: a height from about35 cm to about 50 cm; a nominal diameter from about 10 to about 40 cm;and a first taper angle from about 65° to about 83°.
 2. The air filterbag of claim 1, wherein said first taper angle is from about 78° toabout 83°
 3. The air filter bag of claim 1 further comprising a gusset.4. The air filter bag of claim 3, wherein said gusset comprises a gussettaper angle from about 42° to about 48° and a depth of less than about10.2 cm.
 5. The air filter bag of claim 1, wherein said density is fromabout 20 kg/m³ to about 60 kg/m³.
 6. The air filter bag of claim 1,wherein said air filter bag comprises a non-woven having a thicknessbetween about 1 and about 3 mm, a density from about 20 kg/m to about 60kg/m³, and a pore volume distribution of at least about 15% of the totalvolume is in pores of radii less than about 50 μm, at least 40% of thetotal volume is in pores of radii between about 50 μm and about 100 μm,and at least 10% of the total volume is in pores of radii greater thanabout 200 μm.
 7. The air filter bag of claim 1, wherein said air filterbag is made of a non-woven comprising a total aggregate basis weight ofabout 20 to about 120 gsm.
 8. The air filter bag of claim 1, whereinsaid air filter bag is made of a hydroentangled non-woven having athickness of about 1 mm to about 3 mm.
 9. The air filter bag of claim 1,wherein said air filter has an air flow surface area of about 0.1 m² toabout 1 m².
 10. The air filter bag of claim 1, wherein the face velocityof air exiting said air filter bag is about 6 to about 60 fpm, when saidair filter bag is used with an air filtering device.
 11. The air filterbag of claim 1, further comprising an end-of-life sensor.
 12. An airfilter bag comprising: a height from about 35 cm to about 50 cm; anominal diameter from about 10 to about 40 cm; a first taper angle; agusset comprising a gusset taper angle from about 42° to about 48° and adepth of less than about 10.2 cm.
 13. The air filter bag of claim 12,wherein said first taper angle is from about 65° to about 83°
 14. Theair filter bag of claim 12, wherein said density is from about 20 kg/m³to about 60 kg/m³.
 15. The air filter bag of claim 12, wherein said airfilter bag comprises a non-woven having a thickness between about 1 andabout 3 mm, a density from about 20 kg/m³ to about 60 kg/m³, and a porevolume distribution of at least about 15% of the total volume is inpores of radii less than about 50 μm, at least 40% of the total volumeis in pores of radii between about 50 μm and about 100 μm, and at least10% of the total volume is in pores of radii greater than about 200 μm.16. The air filter bag of claim 12, wherein said air filter has an airflow surface area of about 0.1 m² to about 1 m².
 17. The air filter bagof claim 12, wherein said air filter bag is made of a non-wovencomprising a total aggregate basis weight of about 20 to about 120 gsm.18. The air filter bag of claim 12, wherein said air filter bag is madeof a hydroentangled non-woven having a thickness of about 1 mm to about3 mm.
 19. The air filter bag of claim 12, wherein said air filter has anair flow surface area of about 0.1 m² to about 1 m².
 20. An air filterbag comprising: a height from about 35 cm to about 50 cm; a nominaldiameter from about 10 to about 40 cm; a first taper angle from about78° to about 83°; a gusset comprising a gusset taper angle from about 42to about 48° and a depth of less than about 10.2 cm; wherein said airfilter bag is made from a non-woven having a thickness between about 1and about 3 mm, a density from about 20 kg/m to about 60 kg/m³, and apore volume distribution of at least about 15% of the total volume is inpores of radii less than about 50 μm, at least 40% of the total volumeis in pores of radii between about 50 μm and about 100 μm, and at least10% of the total volume is in pores of radii greater than about 200 μm.